Quran never said that the earth is flat as some ignorant claim, on the contrary, Quran says والأرض بعد ذلك دحاها )( Then after that He made the earth like an egg) (79:30). Dahwah دحوة means in Arabic an egg. Some people translate this verse wrongly claiming that it means spreading it like a flat surface. They need to refer to original word Dahw and Dahwah.
We also read in Quran يكوّر الليل على النهار ويكوّر النهار على الليل(39:5) : He who makes the night like a ball turning on the day, and daylight like a ball turning on the darkness of the night.
Those claim that earth is flat have misunderstood the meanings of Quranic verses.